1. Field of the Invention
This invention relates to an on-chip temperature sensing system, and more particularly, to an improved system, which does not require calibration to account for variations in circuit parameters and connection parameters which inevitably result in the manufacturing process.
2. Description of the Prior Art
There have been a number of prior art proposals for on-chip temperature sensing. These proposals include the use of a pair of on-chip thermally responsive diodes coupled to an off-chip current source. The diode pair generates differential voltage output proportional to temperature. This proposal, and an alternative proposal, that theoretically does not require calibration are shown in IBM Technical Disclosure Bulletin Vol. 28, No. 1, June 1985. Despite the theory, in practice, the output of these prior art circuits, as a function of temperature, varies from one manufactured on-chip circuit to another to an extent that calibration particular to each on-chip circuit is required for satisfactory operation.
The need for calibration of prior art on-chip temperature sensors is a cost factor. Also, calibration of each circuit makes it impractical to implement on-chip temperature sensing in certain applications where it would be desirable. For example, proposals have been made in the prior art to sense the temperature of all the chips in a multi-chip module. The ability to monitor the temperature of all the chips in a multi-chip module has advantages over monitoring the temperature of only sample chips in both module design and manufacturing. Measuring chip temperature on a sample basis results in incomplete and potentially misleading data. Chips not included in the sample can overheat, resulting in component damage which is not detected until significant numbers of failures have been reported. Full sampling enables detection of overheated chips and timely modifications to bring the chips back within a specified operating range. See IBM Technical Disclosure Bulletin Vol. 36, No. 08, August 1993.
The prior art proposed use of an on-chip thermal sensing diode in which the junction voltage varies with operating temperature is a potentially low cost technology for monitoring chip temperature. However, prior art circuits using on-chip thermal sensing diodes have required each circuit to be individually calibrated after it has been manufactured, which adds appreciably to the cost and has made full chip monitoring of multi-chip modules very expensive.